This invention relates in general to the production of steel and in particular to a new and useful method and apparatus for producing steels of great purity and low gas content for special requirements.
The invention relates to a method and the equipment to produce steels of great purity and low gas content for special requirements, whereby the liquid steel is refined with an inert gas in a ladle and the treatment stages decarburization and deoxidation are carried out in a converter.
Various methods to produce steels of great purity and low gas contents are already known.
Best known are melting in the arc furnace or melting in the arc furnace with subsequent decarburization in a converter, using mixed gases or vacuum.
From the energy aspect, producing steels in the arc furnace only is very costly and problematical as far as the purity to be obtained is concerned. Producing such steels in the arc furnace with subsequent decarburization in presently known converters using mixed gases has the disadvantage that these converters, originally designed for the production of chromium steels, have a smaller specific reaction space than is required for the production of the special steels mentioned. Prerequisite for the required high decarburization and heating rate is a large specific reaction volume with a high specific oxygen supply.
Moreover, due to the air entering the reaction chamber, a reoxidation of the melt cannot be avoided during the deoxidation phase.
Furthermore, an intensive air oxygen contact takes place during the pouring of the reduced steel, resulting in disturbing oxidic contaminations, thus leading to scrap in the product.
From the aspect of equipmental and operating sophistication, producing the mentioned steels with subsequent decarburization in a vacuum converter is more complicated and costly.
The above mentioned processes are also difficult to run and require much experience and skilled personnel.
It is further known that in the production of these steels a final treatment in ladles flushed by inert gas can be carried out. But here, too, setting the desired values as to alloy components, temperature, oxygen, hydrogen and purity precisely is not possible, or only with difficulty, if the specified initial values of the arc furnace or of the presently known convertet cannot be set reproducibly.
It is further of particular disadvantage in the three mentioned methods that the desired metallurgical values cannot be set with sufficient accuracy so that material faults are unavoidable which can no longer be tolerated in highly stressed components of installations, such as in nuclear power plants.